This invention relates to the art of measurement and more particularly to a sheet length counter for measuring paper usage in an engineering drawing plotter or other machine having bidirectional paper movement.
It is important to be able to monitor the usage of an engineering drawing plotter, so that media usage and machine wear and tear can be accurately evaluated. Plotters pose two difficult problems.
First, the drawing papers may be of different lengths. Just counting copies does not accurately measure use. Prior counters measured machine and media use in terms of copies made. They were accurate only when material of a known standard size was used.
Second, in plotters, the paper moves backwards and forward with respect to stationary pens. A simple pulse generator, which produces a series of pulses, one every unit of sheet length, cannot distinguish between the two directions. Use of such a counter without correction for paper direction would produce a grossly distorted paper usage report.